A new bathymodioline mussel symbiosis at the Juan de Fuca hydrothermal vents

Until recently, the only major hydrothermal vent biogeographic province not known to include bathymodioline mussels was the spreading centers of the northeast Pacific, but deep-sea dives using DSV Alvin on the Endeavor segment of the Juan de Fuca Ridge (47°56N 129°06W; ∼2,200 m depth) in August 1999 yielded the only recorded bathymodioline mytilids from these northeastern Pacific vents. One specimen in good condition was evaluated for its relatedness to other deep-sea bathymodioline mussels and for the occurrence of chemoautotrophic and/or methanotrophic symbionts in the gills. Phylogenetic analyses of the host cytochrome oxidase I gene show this mussel shares evolutionary alliances with hydrothermal vent and cold seep mussels from the genus Bathymodiolus, and is distinct from other known species of deep-sea bathymodiolines, suggesting this mussel is a newly discovered species. Ultrastructural analyses of gill tissue revealed the presence of coccoid bacteria that lacked the intracellular membranes observed in methanotrophic symbionts. The bacteria may be extracellular but poor condition of the fixed tissue complicated conclusions regarding symbiont location. A single gamma-proteobacterial 16S rRNA sequence was amplified from gill tissue and directly sequenced from gill tissue. This sequence clusters with other mussel chemoautotrophic symbiont 16S rRNA sequences, which suggests a chemoautotrophic, rather than methanotrophic, symbiosis in this mussel. Stable carbon (δ¹³C = −26.6%) and nitrogen (δ¹⁵N = +5.19%) isotope ratios were also consistent with those reported for other chemoautotroph-mussel symbioses. Despite the apparent rarity of these mussels at the Juan de Fuca vent sites, this finding extends the range of the bathymodioline mussels to all hydrothermal vent biogeographic provinces studied to date.     

Welcome

The Association of Environmental and Resource Economists (AERE)is pleased to launch the Review of Environmental Economics andPolicy with this inaugural issue. The need for a new journal aimed toward a broad audience haslong been recognized by AERE members and has been actively discussedfor several years by the AERE Board. The time was finally judgedright to initiate a careful review of the need and prospectsfor such a journal,     

Growth of marine planktonic diatoms on inorganic and organic nitrogen

A study was conducted to determine if coastal diatoms from eutrophic waters (Werribee, Port Phillip Bay, Australia) are able to grow better than diatoms from oligotrophic waters (Bass Strait, Australia) on organic nitrogen compounds as their principal nitrogen sources. Eight clones of marine planktonic diatoms, belonging to 5 species (Skeletonema costatum, Asterionella japonica, Nitzschia closterium, Coscinodiscus sp., and Fragilaria sp.), were incubated with inorganic (either nitrate or ammonia) or organic (either urea, uric acid, alanine, aspartic acid, glutamic acid, glycine, serine, threonine, or valine) nitrogen sources and growth response was measured under high and low light intensities. All clones grew well on the organic as well as thorganic nitrogen compounds under both light regimes. Intraspecific differences were not great, as no appreciable difference was noted between clones from oligotrophic and eutrophic waters. The two negatively-charged amino acids, aspartic and glutamic acids, were somewhat less effective in supporting growth of some clones than were the other amino acids. Virtually all of the dissolved organic nitrogen (DON) compounds tested were utilizable for algal growth. Further, all clones appeared able to utilize at least some natural DON (uncharacterized) for cell division; in 1980, DON represented 97% of total nitrogen in Bass Strait and 83% of total nitrogen in Werribee waters. The results are consistent with previous findings on algal utilization of certain DON compounds and indicate comparable abilities of cells from oligotrophic and eutrophic coastal waters to assimilate these nutrients.Publication No. 307 in the Ministry for Conservation, Victoria, Environmental Studies Series     

Role of filter-feeding in the nutritional biology of a deep-sea mussel with methanotrophic symbionts

The ability of an undescribed deep-sea hydrocarbon-seep mussel which contains endosymbiotic methanotrophic bacteria to clear, ingest, and assimilate radiolabeled bacteria (Vibrio pelagicus andEscherichia coli) and algae (Dunaliella tertiolecta) was compared with that of the bay musselMytilus edulis. The seep mussel, collected in August 1987 from the Louisana Slope in the Gulf of Mexico, was slower to clear bacteria and algae thanM. edulis. The ingestion and assimilation of filtered bacteria and algae was established from the presence of radiolabel in mussel tissues and feces. The seep mussel was somewhat less efficient in assimilating radiolabeled components from bacteria and algae thanM. edulis. The dietary carbon maintenance-requirement of the seep mussel could potentially be met at environmental concentrations of greater than 10⁶ bacteria ml^–1. At lower concentrations of particulate organic matter, filter-feeding could be an important source of nitrogen and essential nutrients not supplied by the endosymbionts.     

The color of the trophosome: elemental sulfur distribution in the endosymbionts of<Emphasis Type="Italic"> Riftia pachyptila</Emphasis> (Vestimentifera; Siboglinidae)

Riftia pachyptila Jones, 1981, lives in association with a chemoautotrophic, sulfide-oxidizing -Proteobacterium that occurs in a specialized organ, the trophosome. Ultrastructurally different bacterial subpopulations occur in different regions of the trophosome lobules (central rods, median small cocci, peripheral large cocci) and contain vesicles, which have been proposed to be sites of elemental sulfur storage. Differently colored trophosomes have been suggested to reflect different amounts of elemental sulfur in the tissue. In this study, the presence of elemental sulfur (S⁰) was confirmed in the vesicles of the symbionts of R. pachyptila by electron energy loss spectrography (EELS). The proportion of (two-dimensional) area occupied by sulfur vesicles in the cells was found to be strongly correlated with trophosome color, both in individuals with uniformly colored trophosomes and individuals that exhibited a gradual color change along the length of their trophosomes. Elemental sulfur content was highly variable between individuals from a single collection, suggesting a high degree of microhabitat heterogeneity within vestimentiferan aggregations.Communicated by O. Kinne, Oldendorf/Luhe     

Countermarking by male pygmy lorises (<Emphasis Type="Italic">Nycticebus pygmaeus</Emphasis>): do females use odor cues to select mates with high competitive ability?

Competitive countermarking occurs when animals compete to ensure that their scent marks are in the top-most position and more recently deposited than those of rivals. Because it takes a great deal of time and energy, and perhaps dominant or territorial status, to patrol the area and rapidly countermark rivals' marks, assessors may use the presence of countermarks as a reliable cue of the signaler's competitive ability. Selection on assessors, therefore, should favor the evolution of mechanisms to determine which scent is the countermark. Sexual selection theory predicts that females select high-quality males with whom to mate; therefore, females should mate preferentially with countermarking males. We examined the role of countermarking in intra-male competition and female mate choice in the pygmy loris. In experiment 1, we found that males deposit significantly more urine when countermarking other males' urine, but countermark female urine no more than control stimuli. In experiment 2, we exposed females to the urine of two males for several weeks. One male always deposited his urine first, whereas the second male always deposited his urine later and on top of the first male's urine. When reaching peak estrus, females were given a simultaneous choice test between the two males, and showed a significant preference for the countermarking male with regard to: (1) her location and orientation to the male, (2) her chemosensory interest in the male and his cage, and (3) her affiliative socio-sexual behaviors. These results are consistent with predictions from the competitive countermarking hypothesis, and demonstrate that chemosignals play a profound role in governing female reproductive behavior in the species.     

Variability of epipelagic macrozooplankton/micronekton community structure in the NW Weddell Sea,Antarctica (1995–1996)

Macrozooplankton/micronekton in the epipelagic zone (0–100 m) of the NW Weddell Sea were sampled with a 10 m² multiple opening-closing net environmental sampling system (MOCNESS) trawl during three cruises in 1995 and 1996. A total of 40 species were collected during all cruises. Community composition, as measured using Bray-Curtis analysis and multi-dimensional scaling, permitted separation into two groups: group 1 included samples collected during September–October 1995 and group 2 contained samples collected during April-May 1996 and November–December 1996. Zooplankton collections were dominated by Thysanoessa macrura in September–October 1995 (high pack-ice cover) and by both Euphausia superba and Salpa thompsoni in April–May 1996 (intermediate pack-ice cover) and November–December 1996 (open water). Copepods were not sampled quantitatively by the MOCNESS trawl and were not included in this analysis. Trends in measured parameters of community structure are discussed with respect to environmental characteristics during each sampling period.Communicated by P.W. Sammarco, Chauvin     

种植密度和降水对冬小麦田N2O排放的影响

为研究种植密度对农田N2O排放的影响和探讨N2O排放季节性波动的原因，于1999～2000年小麦生长季在南京市郊江宁县进行了不同播种量（0.90、180和270kg/hm^2）和大田试验，观测分析结果表明：在相同的气象条件和田间管理下，播种～越冬阶段的N2O排放不受播种量的影响，近青～成熟阶段的N2O排放通量与播种量成正比，裸地条件下的N2O排放与播量为90kg/hm^2下的排放无明显差异，造成该生长季内N2O排放季节性波动的主要原因是降水，返表～成熟阶段的N2O排放通量随观测日前6d的加权平均降水解呈指数增加。     

Metabolic and blood characteristics of the hydrothermal vent tube-worm Riftia pachyptila

Specimens of the hydrothermal vent pogonophoran Riftia pachyptila Jones were collected by submersible at a depth of 2 600 m at the 21°N hydrothermal vent site on the East Pacific Rise (20°50N, 109°06W) in April and May of 1982. The worms were maintained in pressurized aquaria for up to 45 d for metabolic studies. Consumption of O₂ was regulated down to low P_{O 2} (oxygen partial pressure) values; O₂ consumption rates were 0.63 and 1.12 mol g^-1 wet wt h^-1 at 2.5° and 8°C, respectively; such rates were comparable to those previously measured for other pogonophorans. Intact specimens of R. pachyptila (including bacterial symbionts) did not consume significant amounts of CH₄ from the environment. The respiratory quotients, in the absence of added sulfide, indicated that metabolism was mainly heterotrophic. High rates of uptake of dissolved amino acids were recorded for one specimen. The total [CO₂] in the vascular blood and the Hb-containing coelomic fluid were high. Under anaerobic conditions, there were equilibrium distributions of pH, total [CO₂] and sulfide concentrations between the vascular blood and the coelomic fluid, apparently because these metabolites were readily exchanged between the two compartments. The vascular blood bound neither CH₄ nor H₂. However, sulfide was reversibly bound by both the vascular blood and coelomic fluid; because this binding depended strongly on pH (with a maximum at about 7.5), HS^- was probably the molecular species bound. Under anaerobic, but not aerobic conditions, the trophosome bound substantial amount of sulfide; thus, the high concentrations of sulfide in the trophosome may have resulted mainly from sulfide bound to sulfide oxidases under anaerobic conditions. The coelomic fluid had a relatively low buffering capacity (2.2 mmol CO₂pH^-1).